Mineralogical study of weathering products of granodiorite at Shinshiro City (I)

Rock weathering has long been a subject of study for geologists, mineralogists, chemists and soil scientists since the dawn of this century. In methods for investigating rock weathering, three aspects seem to be present. The one is a chemical aspect in which weathering process is considered by comparing chemical composition of fresh parent rock with that of the weathered rock, the difference being attributed to gains or losses of chemica,l elements with respect to a supposed immobile element, usually aluminum. This aspect can elucidate the chemical behaviour of rock, that is, of material as an assemblage of constituent minerals in the environment of weathering. Among many such studies mentioned. PoLYNov's “Cycle of Weathering” (6) is one of the most comprehensive and fruitful acheivements. The second aspect is a mineralogical one, in which interests are directed toward skeletal minerals surviving against severe attacks of weathering. It is commonly observed that some of the original constituent minerals still remain in weathered material after others have been extinguished. The former minerals are more stable than the latter. On the basis of these observations, the sequence of resistantiability or stability to weathering can be determined for many rock forming minerals. GOLDICH's study of rock-weathering (3) is a representative one in this aspect. The third aspect is concerned with clay mineralogy. Primary rock-forming minerals are weathered into very finegrained materials most of which had been believed amorphous until techniques now used in clay mineralogical reserch proved their crystalline state. Besides primary skeletal minerals, weathered materials are now known to consist mainly of both amorphous and crystalline secondary minerals, mostly appearing in minus two micron fraction and being objects of interest in clay mineralogy. Any study of rock weathering hitherto performed stood more or less on the three aspects above mentioned but, all the abovementioned seem to fall into the common tendency of dealing with materials as bulk mass. That is, they were concerned much more with fresh rock versus its weathered end products as a whole rather than with the process or mechanism by which fresh rock changed into weathered material. Thus, in the temperate to subtropical humid region, it is known that, for example, kaolinite minerals, gibbsite, and some of 2: 1 type clay minerals are found in weathered materials of rocks and further that Na, K. Mg. Ca, and Si are leached away, while H, Al, and Fe are concentrated in the weathered products, but it is scarcely understood from what constituent minerals of the parent fresh rock any of the clay minerals now present in the weathered material were derived. Though, a mineralogical or chemical tracing of the courses of decomposing minerals from their initial phases to subsequent modified phases was already pioneered by STEPHEN (8). such a trend is believed, by the author, to be a fourth aspect necessary for further thorough understanding of rock weathering. This way of study may also serve in bridging between experimental data on chemical reactions of specific minerals with reagent solutions on the one hand and observations of mineralogical interrelation of parent minerals to resultant weathering products on the other hand. Granitic rock offers a suitable situation for this fourth aspect because of the ease in picking up mineral grains at various weathering stages due to the coarseness of its constituent minerals and also to its unique mode of physical disintegration.     

Formation of clay from granite and its distribution in relation to climate and topography

Chemical weathering can be approached from three interpretive points of view: distribution of the secondary minerals in landscapes, weathering of primary minerals and geochemistry of ions in solution. On granitic rocks it is posible to define both climatic and topographic sequences of distribution of clays in association with weathering products: gibbsite - kaolinite - hydrous iron oxides - hydrous manganese oxides - iron-rich montmorillonite - calcium carbonate - calcium sulfate - sodium carbonates and silicates. These stages appear as an absolute accumulation formed by filling of intergranular pores. Another sequence can be found not in intergranular pores but in the cracks and along the cleavages of primary minerals from which they are derived by relative accumulation. The order of appearance of these secondary minerals remains the same regardless of the nature of climates and the topographic position. The conditions of equilibrium are not identical in the interior of grains of different primary minerals nor in the pores outside of them and the secondary minerals found in the different situations are also not identical. This is well demonstrated by the chemistry of waters draining slopes. The equilibrium diagrams and balances between cations and silica sometimes result in disagreement, proving that equilibrium conditions are not satisfied between solutions circulating in the pores and clay minerals found inside the primary minerals.     

Mineralogic evolution in hydromorphic sandy soils and podzols in “landes du médoc”, France

Soils of the nearly level “Landes du Médoc” in southwestern France have a pattern of alternating bodies of hydromorphic podzols (Haplaquods) and low humic hydromorphic soils (Psammaquents). The soils are formed in a sedimentary mantle of coarse, quartzose sands with a slight microrelief consisting of low, elongated ridges and shallow, intervening troughs. The water table is at shallow depths throughout the plain, even at the surface in places. The podzols on the crests of the low ridges have distinct A₂ and cemented B₂ h horizons. Podzols persist down the sides of ridges but going downslope first lose the A₂ horizon and then the cementation of the Bh horizon. Soils in the shallow troughs have A₁ and Cg horizons without B horizons.The fine silt (2–20 μm) and clay (0–2 μm) fractions of the parent sand contain primary trioctahedral chlorite, mica, feldspars, and quartz, with the last mineral predominant. During soil development, the first three minerals undergo weathering at different rates and to different extents. Chlorite is most strongly weathered, followed in order by plagioclases and K-minerals. In the fine silt fraction, weathering seems to occur mostly by fragmentation of particles. In the clay fraction, the phyllosilicates successively form irregularly interstratified minerals with contractible but not expandable vermiculitic layers, interstratified minerals with contractible and expandable smectitic layers, and finally smectites.The extent to which the silicate minerals are weathered becomes progressively greater from the low humic hydromorphic soils to the podzols with friable Bh horizons to the podzols with cemented Bh horizons. Smectite is present only in the A₂ horizons of these last podzols.The aluminum release by weathering of silicate minerals is translocated in part in the form of organo-metal complexes into the Bh horizons of the podzols. Greatest concentrations of Al are associated with coatings of monomorphic organic matter on mineral grains in the cemented Bh horizons, in which some Al has also crystallized into gibbsite. That mineral was not detected in friable B horizons of podzols nor in the low humic hydromorphic soil. Contrary to expectations, the mobile Al did not enter interlayer spaces of expanding 2:1 clay minerals.     

The influence of topography on the development of Alfisols on calcareous clayey till in Denmark

A detailed macro- and micro-morphological study of seven closely-adjacent soil profiles on calcareous clay tills in a long-established beech wood in central Denmark, shows that depth of decalcification, thickness of textural B horizon, development of umbric epipedons and development of albic sub-horizons are all related to slope inclination, slope form and to relative situation in the slope complex.The soils may be classified within four subgroups of Alfisols, while one is a Mollisol. The MAST of 8°C poses problems of typification at suborder level between frigid and mesic classes.Development of clay skins and of glaebules and concretions as indicators of the redeposition of mobilised components, are present to greater extent in stable slope situations; with least lateral subsoil water movement. Development of albic horizons is related to greater lateral water movement.Development of cutanic features by argilluviation - argillans - do not exclude features formed by redeposition of carbonates - calcitans. Soil plasmic fabrics with both features are termed calcisepic fabrics and prove deposition of clay and carbonates in the same soil horizons, usually the lower B and C(g) horizons.Morphologically the dark epipedons show intense humification and many fecal pellets because of the undisturbed and high plant productivity and intense biotic activity. The micromorphology is one of isotic argillasepic plasmic fabrics. The argillic horizons are dominantly insepic or vosepic, while the calcareous C horizons are either argillasepic, or calci-vosepic or calcisepic. It is possible that some of the carbonate reprecipitation post-dates the argilluviation, the carbonates derived during secondary dissolution in the suprajacent horizons.     

Investigation of lichens using molecular techniques and associated mineral accumulations on a basaltic flow in a Mediterranean environment

The role of lichens in the breakdown of rocks in various environments is well documented. We investigated the formation of secondary minerals under 13 different fungal species growing on a basaltic flow in Sanliurfa (Turkey) to understand the influence of lichen species on the transformation of minerals in a Mediterranean environment. We used molecular technique (rDNA sequence) to identify 13 different species of lichens (7 crustose, 5 foliose and 1 pathogenic). X-ray diffraction and scanning electron microscopy were used to determine the composition of mineral accumulations. The formation of quartz and 2:1 phyllosilicates in various layers (top, brown and white) of the weathered basaltic flows under all the lichen colonies may be the result of precipitated silica alone (quartz) or in combination with aluminum (2:1 clays) released as a by-product during the breakdown/weathering of primary silicate minerals present in the basalt. However, aeolian deposition may also be a possible source of these mineral species. Whewellite, a calcium oxalate mineral, accumulates in the weathered basalt underneath all the species of lichens. We believe that the formation of whewellite was due to organic acids excreted by fungal hyphae to dissolve primary minerals (e.g., olivine and feldspars); this lichen-mediated process released enough calcium and generated oxalate necessary for the formation of whewellite.     

PLUMBOGUMMITE MINERALS IN A STRONGLY WEATHERED NEW ZEALAND SOIL

Phosphate minerals of the plumbogummite group were tentatively identified in a strongly weathered and leached New Zealand soil formed from granite by comparing changes in inorganic phosphate fractions, after calcination, of a soil sample with those occurring in Christmas Island rock phosphate. This identification was confirmed by X-ray diffraction. Plumbogurnmite minerals were mainly concentrated in the so-called residual organic P fraction with a lesser but significant proportion in the residual inorganic P fraction. Phosphate minerals of this group may be quite common in other strongly weathered New Zealand soils.     

微地形下紫色土的矿物组成和pH的耦合特征

为了研究微地形下紫色土的矿物组成和土壤酸度之间的关系,采集了重庆合川丘陵地区典型的紫色土壤,通过电渗析模拟酸化,并通过X射线衍射光谱分析电渗析前后的矿物组成以及酸度变化。结果表明:不同地形部位的紫色土随着地形部位的降低,土壤原生矿物的比重逐渐降低,土壤的发育程度越来越高。紫色母岩及其发育的土壤pH大小关系为母岩石骨子土半沙半泥土豆瓣泥。pH变化与土壤中的方解石、钠长石和钾长石等矿物的含量有紧密关系。电渗析模拟土壤酸化后发现,石骨子土和半沙半泥土的pH分别降低了4.3,3.8个单位,同时土壤原生矿物分解风化,表明土壤原生矿物(如长石类矿物)可以缓冲土壤的酸化。     

Verwitterung toskanischer Gesteine unter Mitwirkung von Flechten

The role of the lichens in the breakdown of some tuscan rocks In the natural tuscan environment the rocks breakdown by means of the lichens results in the dissolution of primary minerals and not in the formation of neogenesis minerals. Large amounts of Ca-oxalate were found in the weathered sheets of calcareous rocks, while in the ferromagnesian ones the soluble iron oxalate is easily washed away, thus facilitating further weathering. In the lichen sheets the Fe⁺⁺: Fe⁺⁺⁺ ratio is almost constant in contrast with the values found in the rock.     

Micromorphology of zheltozems on hard sedimentary rocks and products of their decomposition: Pedogenic and lithogenic features (with the Sochi arboretum as an example)

The analysis of the microfabric of soils developing from calcareous argillites (with sandstone interlayers) and their derivatives revealed the mechanisms of the transformation of the initial lithogenic features into pedogenic features. They include the release of primary carbonates and their segregation in secondary forms, the redistribution of iron oxides, and changes in the shape of the rock fragments and in the optical properties of the fine material in the lithomarge zone. The subsoil—the metamorphic BM horizon—is characterized by a high content of clay composed of chlorite-vermiculite and mica-smectite minerals along with kaolinite. The BM horizon is compact and has a massive microstructure with clay pseudomorphs over skeleton grains and with nonsegregational forms of iron oxide pedofeatures. The diagnostic properties of this horizon are clearly revealed in the soils on both hard rocks and loose colluvium deposits; in the latter case, they are supplemented with a stagnic marble-like pattern. The integrity of these features corresponds to the elementary pedogenic process of the metamorphism of the mineral mass in humid subtropics. In terms of micromorphology, this is a good example of pedoplasmation. The features testifying to the contribution of biota in the topsoils are few; dark compact nodules are common there. Zheltozems developed from hard rocks may be correlated with Cambisols in the WRB system; zheltozems developed from clayey colluvium display the features of clay illuviation; together with some physicochemical characteristics of these soils, they allow us to qualify such soils as Acrisols. There are also eluvial-gley variants of zheltozems with stagnic features.     

Mineralogy of a podzol formed in sandy materials in northern denmark

This paper deals with possible mineralogical changes from one particle size fraction to another and from one horizon to another in a Typic Haplorthod. X-ray diffraction and chemical analysis were the main methods used. The investigation indicates that a large part of the fine material in the soil is developed during weathering in situ. Less resistant minerals seem to be protected by being parts of rock fragments in coarser fractions, but once freed from that protection they quickly undergo fragmentation into finer particles. Most of the sand and silt fractions are quartz. The K-feldspar content ranges between about 10 and 20%, the Na-feldspar content from about 15 to 30% and the Ca-feldspar content is very small. The clay minerals are mostly kaolinite and mica and in the A2 horizon, expandable 2:1 minerals containing both smectite and vermiculite layers. The B horizon contains 14 A minerals that resemble interstratified vermiculite—chlorite. In the C horizon both vermiculite—chlorite and clorite occur.     

我国北亚热带白浆化土壤矿物学特性的研究

本文对北亚热带地区七个白浆化土壤的原生矿物和次生矿物的特性进行了研究。重，轻矿物含量表明土壤继承了母质的特性，粘淀层与漂白层的母质沉积是间断的，前者风化强度大于后者。石英颗粒表现特征显示漂白层物来来源于黄土物质再堆积，粘土矿物以水云母为主，其结晶度较差，氧化铁类型以针铁矿和赤铁矿为主，也有非晶质氧化铁和硅酸盐中的Ｆｅ＾２＋，其形成条件与现代化成土条件一致。     

Differences in silica release from soils of two Scottish associations as assessed by trimethylsilylation

The amounts of monomeric silica released on trimethylsilylation of a range of Soil Groups of the Darleith Soil Association, developed on glacial till derived from Carboniferous age lavas of basic and intermediate composition, is significantly higher than the amounts released from corresponding Soil Groups of the Lauder Soil Association, developed on glacial till derived from Devonian age conglomerates and sandstone. Monoremic silica release values for the leached soils within an association are, in general, higher than those of the gley soils. For all soil profiles the eluvial horizon released the smallest amount of monomeric silica with the maximum amount being released, in most instances, from the illuvial horizon. Ferromagnesian minerals and crystalline clay minerals, in particular vermiculite and chlorite in the Darleith Association soils, release monomeric silica under acid conditions. For both the Darleith and Lauder Association soils the principal source of monosilicic acid is thought to be aluminosilica gel of low Si:A1 ratio.     

Mineralogical study of weathering products of granodiorite at Shinshiro City (IV)

In the preceeding paper(1), the weathering sequences of each primary mineral were established in the weathering profile of granodoritie mainly by X-ray diffraction analysis of the weathered mineral grains coarser than 0.2 mm. Since the silt and clay fractions were assumed to have been produced by disintegration or decomposition of the primary minerals as seen in the former papers (2, 3), there should be genetical interrelation between the mineralogical compositions of the silt and clay fractions and the onen of the weathered grains of the primary minerals.     

Genesis and dynamics of an oxic dystrochrept and a typic haploperox from ultrabasic rock in the tropical rain forest climate of south-east Brazil

Oxisols are a product of long and intense weathering. Their actual characteristics can neither be traced back to a certain climatic period, nor do they reveal the present soil-forming factors. In this paper, therefore, a reconstruction of the soil genesis of a strongly weathered Oxisol is attempted by comparing the present mineralogical status and the recent dynamics of selected elements with a nearby Inceptisol from the same catena. The parent rock of both soils is serpentinized dunite with nepheline-syenitic veins; the soil moisture regime is udic. Chemical and mineralogical parameters, as well as the concentration of elements in the soil solution of a Typic Haploperox and an Oxic Dystrochrept from the same catena were analyzed for one year. The dynamics of Si and Mg strongly depended on the state of weathering. In the saprolite of the Dystrochrept, Si is partially removed and partially fixed by the formation of quartz and mixed layer minerals. Mg is first fixed in mixed layer minerals, but is during consecutive weathering leached from the transition zone from saprolite to the oxic horizon. Due to the high redox potential, Fe is not soluble, forming goethite in the upper part of the saprolite. Al is also not removed and is finally fixed in kaolinite. In the weathered upper part of both profiles the concentration of Al, Si, Mg and Fe in the soil solution is too low to perceive a further weathering. The present dynamics of Fe, Al, Mg and Si and the mineralogical status of the Dystrochrept indicate that these processes are similar to those that have led to the formation of the Haploperox. The soils, therefore, developed exclusively by the relative enrichment of Al and Fe, the partial loss of Si and the almost complete loss of Mg. Desilification and ‘laterisation’ are hence processes occurring also presently under a tropical rain forest climate.     

Early stages of pedogenesis at the bottom of a 30-year-old artificial depression under semidesert conditions

Initial soils that developed at the bottom of an artificial hollow 30 × 40 m in size and 3 m in depth have been studied. The hollow was dug on a plot with a predominance of solonetzic complexes in the soil cover on the territory of the Dzhanybek Research Station in 1979. A soil with a shallow but clearly differentiated profile composed of a litter, a humus-accumulative W horizon leached from carbonates, and an underlying C1ca horizon with a high content of dispersed carbonates formed in the hollow over 30 years. The total thickness of these horizons is 7–10 cm. The morphology of the profile corresponds to the slightly alkaline humus-accumulative calcareous soil type of the order of immature soils in the current classification of Russian soils. The soil-sediment layer to a depth of >80 cm contains little soluble salts, predominantly sulfates; the content of exchangeable Na does not exceed 1 meq/100 g. Groundwater of calcium sulfate composition occurs at a depth of ～3.8 m. These features, together with additional moistening by low-saline melt water, ensure favorable conditions for the spontaneous propagation and development of herbaceous, shrubby, and woody plants in the bottoms of artificial hollows. The development of a soil profile is accompanied by the depletion of the clay fraction from the upper W horizon, presumably due to the predominant removal of smectite minerals. In the upper W horizon, transformations of layered aluminosilicates takes place: it involves the formation of illites from smectites and from smectitic layers in illite-smectite mixed-layered minerals and partial vermiculitization of chlorites. The technology used upon the excavation of the hollow can be recommended for growing woody-shrubby plants on soils of the solonetzic complex in the clay semidesert during a relatively short time period.     

Weathering of gneiss in Calabria,Southern Italy

The effects of weathering in a Mediterranean climate on the mineralogy and microfabric of Paleozoic gneiss of the Sila Massif, Calabria, southern Italy, have been studied. Field observations show highly weathered rock forms a residual soil. Micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages, having two distinct rock microfabrics. In the first stage, the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing, and large portions of the rock remain unaltered. The second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals. This latter stage occurs along both compositional and microstructural discontinuities, with etch pitting of feldspar, and neoformation of clay minerals and ferruginous products replacing feldspar, biotite, and iron-bearing garnet. The determination of quantitative petrographic indices provides a measure of the various stages of weathering.     

中国土壤胶体研究—Ⅶ.内蒙暗栗钙土的粘土矿物

内蒙栗钙土区属半干旱而温和的大陆性气候,年平均温度-2.4-6.5℃,冬夏温差很大,约差30-49℃,夏季平均温度为20-25℃,比黑钙土地区高,年降水量200-350毫米,多集中夏季。由于气候干旱,相对湿度很低,蒸发量大于降水量数倍,大陆性气候十分明显。植被以禾本科草及篙属的短草为主。地形主要为高平原,包括一部分丘陵岗地。     

THE ORIGIN AND DEVELOPMENT OF CLAY-WITH-FLINTS AND ASSOCIATED SOIL HORIZONS ON THE SOUTH DOWNS

Clay-with-flints rests on remnants of the exhumed sub-Eocene surface, which is shown to be an important geomorphological feature of the West Sussex Downs. Mineralogical and other soil profile studies indicate that the deposit has developed by the action of cryoturbation and soil-forming processes on a thin cover of Reading Beds clay left on the sub-Eocene surface during the southward recession of a small Eocene escarpment. Two horizons corresponding to Clay-with-flints sensu stricto of Loveday (1962) are recognized. The basal horizon is composed partly of insoluble Chalk residue, but mainly of clay moved down from overlying horizons into the spaces left on dissolution of the Chalk at the junction of the Chalk with the base of the Clay-with-flints. The upper horizon is composed of material from weathered remnants of Reading Beds clay, thoroughly mixed by cryoturbation with flints, other insoluble Chalk residue and clay from former basal horizons. The surface horizons of the soils often include additions of loess.     

南极半岛海洋气候区的土壤Ⅶ. 矿物学特性

南极海洋气候区岩石风化和土壤形成过程中有明显的原生矿物蚀变作用和自生矿物成矿作用。本文以粗骨寒冻灰化土和石灰性扰动冻土两种有代表性的土壤类型为例,阐述了本区土壤矿物学特征。指出铝氧化物、绿泥石、碳酸盐是本区玄武岩类风化物质上发育土壤中的主要自生矿物类型,蒙脱石、特别是绿泥-蒙脱石混层矿物是南极海洋气候区土壤粘粒部分的特征矿物。不同土壤由于成土环境、成土过程、成土历史的差异,其土壤物质的矿物学组成、含量、形态、分布具有明显不同。土壤发生性铁氧化物与成土作用和土壤过程密切相关,其矿物类型、含量、形态特征、分布模式在不同的土壤中明显不同,是表征土壤发育程度与剖面形态表达的有效指标。     

Influence de gels mineraux et d'argiles sur la cristallogenese du carbonate de calcium a partir des solutions bicarbonatees

The precipitation of calcium carbonate is obtained from a bicarbonate solution added with silica gels, silico-mangnesian gels, ferric gels and clay minerals.Two methods have been performed. The first one consists of a quick removal of CO₂; the second one refers to settled solutions. Identification of various carbonates is obtained by infra-red spectroscopy. Morphology of crystalline shapes are analysed with scanning electron microscope.It is etablished:

(i) silica gels are not good inhibitors of calcite;

(ii) silico-magnesian gels reduce the time of precipitation and promote the deposition of “disordered” calcite (intermediate hydrated form between amorphous calcium carbonate and calcite) and (OH) aragonite;

(iii) ferric gels inhibit very strongly calcite; then, vaterite and aragonite are deposited;

(iv) at the least, the presence of clay minerals promote the stabilization of amorphous calcium carbonate and “disordered” calcite.

The gels and the minerals which are here tested and recognized in soils take therefore an active part in the kinetics of precipitation and in the nature of the calcium carbonates.